The present invention generally relates to a semiconductor apparatus, and more particularly, to a circuit provided with an internal power generating means within the semiconductor so as to switch the internal power voltage from the outside when an acceleration test or the like is effected.
The power voltage of CMOS LSI is desired to be 5 V unit as TTL is a power voltage 5 V. But the minuteness of the LSI is desired to be advanced and also, the power voltage is also desired to be scaled in terms of reliability and so on. As one of the solving methods of the above described problems, a system where an internal voltage generating circuit is provided in the LSI with an external voltage being 5 V, the operation is effected with the internal voltage being 3 V.
When acceleration tests by high power voltages such as burn-in tests are tried with respect to the semiconductor apparatus using the system, an acceleration test cannot be effected, because the power voltage is not increased as expected, if the external voltage voltage is made higher within, due to an internal power voltage generating circuit. Therefore, a power circuit with such an external power voltage detecting circuit attached to it as the internal power voltage is switched into an external power voltage from the output of the inner power voltage generating circuit when the external power voltage becomes a certain voltage or more in a burn-in test or the like.
FIG. 10 is a block diagram of an conventional internal power circuit with an external power voltage detecting circuit. Referring now to FIG. 10, reference numeral 1 is an external power voltage detecting circuit, reference numeral 2 is an internal power voltage generating circuit, reference numeral 3 is a power voltage switching circuit, reference numeral 4 is a power voltage switching signal, reference numeral 6 is an output of a power circuit.
An operation of the conventional power circuit constructed as described hereinafter will be described.
When the external power voltage VCC stays within the normal operation voltage range of the semiconductor apparatus, the external power voltage detecting circuit 1 outputs a "L" level (low voltage level) as a power voltage switching signal 4. Voltages generated from the internal power voltage generating circuit 2 are outputted to the output 6 by a power voltage switching circuit 3. When the external power voltage VCC has become a voltage of the normal operation power voltage or more in the burn-in tests or the like, the external power voltage detecting circuit 1 outputs a "H" level (high voltage level) as a power voltage switching signal 4 so as to connect the external power VCC to the output 6 by a power voltage switching circuit 3.
In such conventional construction as described hereinabove, it takes much time until a correct power voltage switching signal 4 is outputted when the external power voltage detecting circuit 1 puts the power supply to work. As shown in FIG. 11, the power voltage switching signal 4 rises together with the rise of the VCC, and the correct output of the external power voltage detecting circuit 1 is effected after a while. The power voltage switching circuit 3 has a disadvantage of outputting the external power voltage at the early stage of the power supply to be put to work. When the external power voltage is outputted at the power transfer, there is a problem that the reliability of the semiconductor apparatus is deteriorated.